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TERRESTRIAL TEMPERATURE. 



TERRESTRIAL TEMPERATURE. 



186 



Comparative Climatology." In this hope he was no doubt fully 

 justified, but one of the most profound of his followers, Professor Dove 

 of Berlin, was led to the conclusion, as the result of the tabulation of 

 an enormous mass of observations, (' Meteorologische Untersuchungen,' 



Berlin, 1837; ' Temperaturtafeln, 1 1849; ' Die Verbreitung der Wiirme 

 auf der Oberflache der Erde,' 2nd edit., 1853 ; ' Klimatologische Beitrage,' 

 1857, &c.,) that it was necessary, in order to understand the true climate 

 of a| place, to carry this system of lines of equal temperatures much 



beyond those of annual and semi-annual periods, there being between 

 places of nearly the same mean annual temperature sometimes very 

 remarkable monthly variations, and to which are due the most marked 

 differences in the general character of the climate and natural pro- 

 ductions of the respective places. Dove in short concluded that it was 

 necessary to have a complete series of Monthly Isothermalt, a name 

 he judiciously adopted for the curves connecting places having equal 

 temperatures in the same month, instead of carrying further the 

 terminology of Isotheral and Isocheimal: the lines of equal annual 

 temperatures he proposed to call Yearly Isnthrrmalt instead of simply 

 isothermal* with Humboldt. Of these Monthly Isothermals, Dove has 

 given separate maps on the equatorial projection for each month, and 

 combined polar and equatorial maps for January and July. He has 

 also carefully observed and laid down in a series of maps the monthly 

 thermal anomalies, uniting them by lines wbich he terms Iiabnormalt. 

 Indeed Jbis maps, tables, and memoirs altogether present a surprising 

 man of information on this branch of science, with the greatest 

 precision and clearness. In his essay on ' The Distribution of Heat 

 over the Surface of the Globe,' translated for the British Association, 

 he arranges the different Monthly Isothermals which he has established 

 into four classes : 



"1. Isothermals which are always found in pairs, intersecting both 



hemispheres : this class includes all between 32 and 77 Fahr. 

 " 2. Isothermals which are sometimes single and sometimes in pairs, 

 that in, sometimes intersecting one or other hemisphere only, and 

 sometimes both : to this class belong many of the isothermals 

 below the freezing point, and some of those of highest tempera- 

 ture which do not pass through all meridians, for example, 

 81'5 Fahr. 



" 3. Isothermals which always occur singly (or in one hemisphere 

 only), at a particular season, not touching it in other parts of the 

 year : to this class belong the isothermals of lowest, and also 

 those of highest temperature (40 and 90'5 Fahr.) which are only 

 developed at particular seasons, and enclose detached spaces. 

 " 4. Lastly, the isolated patches of highest temperature which are 

 developed at particular places in the torrid zone, without passing 

 through all meridians, and are enclosed by isothermals that fork, 

 that is, divide into two branches, (76'25, and 81'5 Fahr.)." 



Having thus briefly indicated the character of the several Isother- 

 mal lines, we refer back to the articles CLIMATE and METEOROLOGY, 

 where, and in the connected articles there referred to, the circumstances 

 which appear chiefly to regulate the temperature of the earth will be 

 found discussed at length ; also various details illustrative of the 

 temperature of different parts of the earth's surface ; together with 



tables of the mean temperatures in different latitudes, as well as 

 formulae expressive of the most important general results. We shall 

 in this place merely add that Dove has deduced as the result of his 

 tabulation of innumerable observations, that the mean annual tempera- 

 ture at the surface of the earth is in January 48'9 Fahr. in the 

 Northern, and 59'5 in the Southern hemisphere, giving a mean of 

 54'2 for the whole earth ; while in July it is 70'9 Fahr. in the 

 Northern and 53'6 in the Southern hemisphere, or 62'3 for the 

 whole earth, thus showing an increase of 8 Fahr. from January to 

 July. Again if we take "the mean between the temperatures of 

 January and July for the northern and southern hemispheres 

 respectively, we 6nd for the northern hemisphere 59'9, and for the 

 southern 56-5 Fahr., being 58-2 for the whole earth." Further he 

 has found that in all seasons of the year there is encompassing the 

 whole earth a zone having a temperature above 77 Fahr. 



The following tables, by Dove, show the mean annual temperatures 

 at different degrees of latitude in the two hemispheres, and the 

 mean annual decrease of temperature from the equatorial to the polar 

 regions : 



MEAN ANNUAL TEMPERATURE OF THE NORTHERN AND 

 SOUTHERN HEMISPHERES. 



DECREASE OF TEMPERATURE FOR THE ENTIRE EARTH. 



We now turn to the distribution of the atmosphere over the sea. 

 [SEA.] It is a well established fact, that places near the sea have a more 

 uniform climate than those which are at great distances from it, though 



